Mordechai Ben Daniel, Welcome to mi.yodeya, and thanks very much for the interesting question! I look forward to seeing you around.
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Isaac MosesDec 1 '10 at 20:08

Keep in mind that one is not allowed to start Shabos at a later time than the community's latest starting time. So if you "prove" that candle lighting should be 3 minutes later than the time that the community lights, you still can not start Shabos later than when the community does if you proof is not accepted. But if you are on the road or stuck in an airport outside of a city, start calculating - You may even want to use Rabeinu Tam time :-)
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inSeattleDec 6 '10 at 4:03

@YDK - adjust it for what? IIUC, the 18 minutes are a sort of buffer zone to ensure that Shabbos won't be violated. That doesn't change depending on where a person is located.
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DaveDec 2 '10 at 3:47

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@Sam - Unless you're way above sea level, like in an airplane, altitude won't have a significant effect on the time of sunset. A more complicated question is how to deal with mountainous terrain; see this link for a comprehensive discussion about it: chaitables.com/chaiintro.html
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DaveDec 2 '10 at 4:25